how!!!

how do i buy without my parents knowing

Relatively speaking, the buying is the easy part. Go to a store and buy if those diapers will do it for you. If you order, use a prepaid gift card. You can have shipments sent to UPS stores for pickup if it's too risky to have a home delivery. Keeping them hidden once you have them is often the more troubling matter. Be sure you've got a spot that's solid to hide them if this is something you really want and you really don't want to be found out. Being an ABDL living in a hostile environment is something like being a spy. Consider the risks and contingencies. It might just be that it's too risky for whatever enjoyment you might get from them. I hope you can choose wisely.